I have "September Charm" and "Honorine Jobert" in the front border (part-shade). They slowly form a clump. As Betty said, their rate of growth depends on the soil and the amount of fertilizer. I give them a small sprinkle of bulb fertilizer in the Spring.

Planting them next to a woodland would be lovely but they aren't "invasive" in a garden bed.

I wish I would get some "volunteers"...my plants seem to really struggle...out of the three I planted two years ago..only one of them is really worth the space it takes up....but I do love them and will keep trying to get a nice healthy plant.